Switched reluctance drives are controlled by switching the phase currents on and off in synchronism with the rotor-position. Usually, this synchronism is achieved by feeding back the rotor position to the controller using a shaft position sensor such as a resolver or an optical encoder. Shaft sensors are not always sufficiently robust. Considerable work has been done on estimating rotor position in switched reluctance drives in order to eliminate the shaft position sensor. The most comprehensive of these approaches involves the use of either a flux/current map, as described in commonly-assigned U.S. Pat. No. 5,097,190 to J. P. Lyons and S. R. MacMinn on Mar. 17, 1992, (e.g. lookup tables) or a solution of a lumped parameter flux/current model, as described in commonly-assigned U.S. Pat. No. 5,107,195 to J. P. Lyons, S. R. MacMinn, and M. A Preston on Apr. 21, 1992, to determine rotor position. Both non-intrusive techniques derive a position estimate from stator flux-linkage and current of the torque producing phases. Machine stator flux is estimated by integrating the quantity (v-iR).
In commonly-assigned U.S. Pat. No. 5,325,026 to J. P. Lyons, S. R. MacMinn, and A. K. Pradeep on Jun. 28, 1994, these techniques are extended to low rotational speeds where the torque-producing current pulses are of sufficient duration to allow for significant error to accumulate in the flux integrators. These techniques eliminate the need for the shaft position sensor by solving models of the magnetic characteristics of the switched reluctance machine (SRM) in real-time. However, this can add a significant computational burden to the control processor, particularly for the high speed applications encountered with aircraft motors and generators. The increased computational requirements can lead to the use of expensive digital signal processors or the added expense of an additional processor dedicated to the shaft position estimation algorithms.
Commonly-assigned U.S. Pat. No. 5,525,886 to J. P. Lyons and M. A. Preston on Jun. 11, 1996 describes a method for estimating rotor position of a switched reluctance motor during rotor startup of low speed operation by applying a sequence of high-frequency, short-duration electric probing pulses to at least two inactive excitation phase windings of a multi-phase motor.